There has been considerable interest in recent years in nonaqueous cells because of the possibilities they afford of obtaining cells which are especially useful for small electronic applications, for example, calculators, circuit boards, and watches, because of their desirable characteristics such as high energy and volume density. Such cells would also overcome some drawbacks, for example, the self discharge and relatively low voltage, of the presently widely used nickel-cadmium cells. Nonaqueous cells may be either primary, that is, they are manufactured in the charged state and undergo only discharge, or secondary, that is, they are capable of being recharged after discharge.
Many materials have been considered as candidates for the electrode materials in nonaqueous cells. The negative electrode typically comprises an alkali metal such as lithium or sodium although other materials have been considered. The positive electrode is selected from many classes of materials. Members of the class of materials that undergo topochemical reactions are potentially useful as the active positive electrode materials in secondary cells and have thus received particular attention. Topochemical reactions may be broadly defined as those reactions that involve a host lattice into which a guest species is inserted with the resulting structure maintaining the essential structural features of the host lattice. In many topochemical reactions, the structural changes are minimal and the process is termed intercalation. The intercalation process is likely to be readily reversible and may form the basis for a secondary cell if the reaction is of the oxidation-reduction type.
Topochemical reactions of alkali metals and several types of transition metal compounds are presently especially promising candidates for use in secondary cells. The use of the layered transition metal selenides and sulfides as the active positive electrode materials in such cells has received much attention. However, other factors being equal, the transition metal oxides are more desirable electrode materials than are the sulfides and selenides because they afford higher energy densities per unit weight and/or per unit volume. Additionally, the oxides are less noxious on decomposition than are the sulfides and selenides.
Several families of transition metal oxides have been studied for use as electrode materials. For example, V.sub.2 O.sub.5 has been used in a primary cell by Dey et al. as disclosed in U.S. Pat. No. 3,655,585, as well as by Walk and Gore in Electrochemical Society Meeting, Paper No. 27, Toronto, May 11-16, 1975. However, these materials are not generally of great interest for use as electrode materials in secondary cells because they suffer from irreversible reduction at low potentials as well as electrolyte oxidation during charging. Vanadium oxides, including VO.sub.2 (B) and those having the nominal stoichiometry VO.sub.2+y, y greater than 0.0 and less than or equal to 0.4, have been used in secondary cells as described by Christian, DiSalvo, and Murphy in U.S. Pat. No. 4,228,226. These oxides have open and closely related shear structures which facilitate topochemical reactions with lithium. Several tungsten oxides have been shown to undergo topochemical lithium incorporation. See, for example, K. H. Chang and M. S. Whittingham, Solid State Ionics, 1, pp. 151-156 (1980). Transition metal oxides, such as RuO.sub.2, OsO.sub.2, IrO.sub.2, MoO.sub.2, WO.sub.2 and VO.sub.2, having the rutile structure have been used as the positive electrode material in secondary lithium cells by DiSalvo and Murphy as disclosed in U.S. Pat. No. 4,198,476.